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"Veritasium" (YT) - "The Big Misconception About Electricity" ?
Zero999:
--- Quote from: SandyCox on December 30, 2021, 09:18:44 am ---
--- Quote ---In a lossless transmission line, energy won't be lost due to radiation.
--- End quote ---
I used to think so as well. However, the following paper:
J. E. Storer and R. King, "Radiation Resistance of a Two-Wire Line," in Proceedings of the IRE, vol. 39, no. 11, pp. 1408-1412, Nov. 1951, doi: 10.1109/JRPROC.1951.273603.
shows that a lossless transmission has a finite radiation resistance.
--- End quote ---
It depends on what is meant by lossless. If it has zero resistance, but is unshielded, then you're right, it will act as an antenna and radiate, but if it's perfectly screened as well, then it will not radiate.
Interestingly, this antenna will have several resonant modes, which will be excited, not only due to the length and separation of the wires, but the diameter of the conductor itself, which isn't stated.
Sredni:
--- Quote from: EEVblog on January 01, 2022, 09:12:31 am ---Nope, still not telling me anything useful, just stating that's a way to look at it.
What can looking at it that way DO FOR ME?
--- End quote ---
And what does thinking the power flows in the cable do for you? If all you want to see is voltage and current, you don't need that information either.
When you have to power a 1kW heater, do you look for a cable capable of sustaining 1kW of power? You just need to dissipate the power associated with the Poynting vector impinging in the cable.
Which makes me think of a way to verify if power comes from... outer space. Nope, surface charge will prevent that and make sure the Poynting vector, as soon as we cross the lateral surface of the resistor, will be directed inward in a uniform way (in hindsight it's logical if we consider that the E field inside is constant and directed along the axis).
Off the top of my head, knowing the Poynting vector field might help knowing which part of your heater will be hotter. If the battery-resistor circuit is not symmetric the power getting into the resistor (to be dissipated) will not follow a symmetric spatial distribution. In the improbable case you can have a perfectly homogeneous resistor, it should be possible to see certain parts of the heater glow more, while others will glow less. I wonder if its doable or if the process of redistribution in the material will make this effect drown in a sea of thermal uniformity.
--- Quote ---Do you have any comment on how quantum field theory views this? or do you think it's bunk?
--- End quote ---
You don't need to go as far as QFT to muddy the waters. Even plain quantum mechanics can make things so complicated that you won't be able to have intuitive insights. For example: what makes the above heater glow? A classical physicist would say it's the collisions of electrons with the material's atomic lattice. A quantum physicist will object to that: what electrons? There's a collective wave function there, not a bunch of identifiable electrons. And if you have a perfectly spaced lattice that wave won't interact at all, so it can't be the lattice. Turns out it's imperfections in the lattice and the mechanism behind the transferal of energy is electron-phonon interaction. You need to throw in more than half Ashcroft Mermin to explain why your heater glow.
Back to QFT. My understanding is that more advanced theories can extend our knowledge to explain more of what we observe. So the question is: will QFT give different values for the electric and magnetic field in the space around the wires? I doubt it. These fields can be measured, so if QFT is that good of a theory they say (and it is) it will agree with experimental measures.
Do you think that the value of the electric and magnetic field in the middle of a circuit with battery and resistor will be different from what is predicted by classical ED? (I am not talking about vacuum fluctuation, but fields of the order of magnitude we can measure with 'ordinary' instruments).
EEVblog:
--- Quote from: Sredni on January 01, 2022, 11:25:40 am ---You don't need to go as far as QFT to muddy the waters. Even plain quantum mechanics can make things so complicated that you won't be able to have intuitive insights.
--- End quote ---
Let me replace the text:
--- Quote ---You don't need to go as far as QFT Poynting to muddy the waters. Even plain quantum mechanics Poynting Thereom can make things so complicated that you won't be able to have intuitive insights.
--- End quote ---
You are now saying the same thing that many people say about Poynting/Maxwell for DC and LF.
It's turtles all the way up.
EEVblog:
--- Quote from: Sredni on January 01, 2022, 11:25:40 am ---Back to QFT. My understanding is that more advanced theories can extend our knowledge to explain more of what we observe. So the question is: will QFT give different values for the electric and magnetic field in the space around the wires? I doubt it. These fields can be measured, so if QFT is that good of a theory they say (and it is) it will agree with experimental measures.
Do you think that the value of the electric and magnetic field in the middle of a circuit with battery and resistor will be different from what is predicted by classical ED? (I am not talking about vacuum fluctuation, but fields of the order of magnitude we can measure with 'ordinary' instruments).
--- End quote ---
I am not talking about the measurements, they will be as they always have been. I'm talking about the the title of this thread "The Big Misconception About Electricity". Does the energy flow in the field around the wire or does it flow in the wire at DC? Poynting/classical field theory says outside, QFT appears to say inside.
I want to know what you and others who have been so (not incorrectly) dogged about anyone that dares think of this in any other way than Maxwell/Poynting think about this apparent conundrum.
bdunham7:
--- Quote from: Sredni on January 01, 2022, 11:25:40 am ---And what does thinking the power flows in the cable do for you? If all you want to see is voltage and current, you don't need that information either.
--- End quote ---
As far as the work of an engineer regarding a DC circuit--specifying parts and calculating losses--the concept of 'power flow' probably doesn't factor in. However, it helps to understand it intuitively when you are deciding what to worry about. So if your cable has to run through a metal tube or take some odd shape, you need to know whether to consider 'the spaces in between the wires' and all that. For an all-DC device--say battery powered thermal socks--the answer is you need not worry at all. For a mains-powered toaster, you need to understand the magnitude of certain effects (primarily induction in surrounding objects) to know that you don't need to concern yourself with 'the spaces between' for the actual toaster and its cord, but you do have to construct your house wiring following certain rules, such as not having only one of a pair of current carrying conductors be within a metal conduit. For a USB-3 circuit board, it's more 'spaces not traces', although that's not a definitively accurate statement either.
--- Quote ---When you have to power a 1kW heater, do you look for a cable capable of sustaining 1kW of power? You just need to dissipate the power associated with the Poynting vector impinging in the cable.
--- End quote ---
Of course not and that is just another of your ridiculous straw men. The cable needs to dissipate the power associated with the required current and the cable's resistance. Somehow determining that by calculating Poynting vectors and an S-field would be the most ludicrously obtuse way that I can think of. Here is a completely solved thermal sock circuit. What I see is a circuit with its behavior completely defined regardless of how you configure the wires and regardless of what is in the 'spaces between', except perhaps a varying magnetic flux. How would you apply Poynting to this in any helpful way?
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